This invention relates to semiconductor light emitting devices of a lamp or chip type. More particularly, this invention relates to a semiconductor light emitting device provided with a protecting element for protecting a light emitting element chip from being damaged by reverse voltages or the like, even where the light emitting element is applied by reverse voltages or high forward voltages.
The conventional semiconductor light emitting devices have been structured by a p-n junction having a direct junction between a p-type layer and an n-type layer or a doublehetero junction having an active layer sandwiched between p-type and n-type layers, so that light can be emitted by the p-n junction or the active layer by applying a forward voltage to between the p-type and n-type layers.
The lamp-type light emitting device, as shown in FIG. 30, includes a light emitting chip (hereinafter referred to as "LED chip") 3 with semiconductor layers that is die-bonded on a curve-surfaced recess portion provided at a tip of a first lead 1. The LED chip has one electrode formed at its bottom face electrically connected to the first lead 1 and the other electrode formed at its top face electrically connected to a second lead 2 via a gold wire 4 or the like. These elements are molded by a resin package 6 transperent for the light emitted by the LED chip 3.
Meanwhile, the chip-type light emitting device, as shown in FIG. 31, is widely used as a light emitting source for portable appliances, such as handy telephones and PHSs, that have to be made small in sized and light in weight. That is, the device has a base plate 91 having terminal electrodes 92, 93 formed at respective end portions thereof. One of the terminal electrodes 92 has an electrode portion connected thereto to have an LED chip 3 die-bonded thereon so that a bottom electrode of the LED chip is directly connected with the terminal electrode 92. The LED chip 3 also has a top electrode wire-bonded to the other terminal electrode 93 via a gold wire 4. Thus, electrical connections between the electrodes are made. The base plate 91 is molded on a main surface side so as to encapsulate the LED chip 3, the gold wire, and so on, thus forming a package 95.
These light emitting devices are of a diode structure so that they have no electric current therethrough where a reverse voltage is applied thereto. There is an adopted method of usage utilizing such a rectifying function, wherein an A.C. current, instead of a D.C. current, is applied to the device so as to allow an electric current to flow therethrough only while a forward voltage by the A.C. current is applied.
The usual semiconductor light emitting chip generally employs a compound semiconductor based on such as GaAs, GaP and gallium-nitride. However, where such a compound semiconductor is used, the resulting chip is less resistive to reversely applied voltages and accordingly susceptible to suffer damages in its semiconductor layers. In particular, where using a gallium-nitride based compound semiconductor having a high bandgap energy, the device has a higher operating voltage as compared to a device with a GaAs chip. Further, the device has a low withstand voltage with respect to reverse voltages and is susceptible to suffer damages due to the reversely applied voltage. Thus, there is a problem that the device is damaged or deteriorated of characteristics by applying an A.C. voltage
On the other hand, even where no A.C. voltage is applied for driving the device, there is also a problem that when a high voltage such as a surge voltage is externally applied, there is a possibility that the compound semiconductor junction be damaged even if the voltage is in a forward direction.